More than a quarter of all year 10 students and half of all year 12 students in Australia are sexually active. Most young women don't seek prescription contraceptives until about a year after their first sexual encounter, however half of all teenage pregnancies occur during a female's first six months of sexual activity.

"There are a lot of myths around the dangers and side effects of contraception but for most women, most methods are perfectly safe, it's just a matter of finding the right one to suit you," says Dr Caroline Harvey, medical director of Family Planning Queensland (FPQ).

Factors that will affect your choice include your lifestyle; your relationship status; how important it is for the method you use to be effective; how quickly reversible it is; what the side effects are; how confidential you want to be about your method; the cost; and how easy is it to get.

"Young women are often highly fertile but for the most part they use methods that require diligence daily or each time they have sex," says Caroline. "If you want something highly effective then certainly look at some of the long-acting methods."

It's important to remember that only condoms provide protection against sexually transmitted infections (STIs). If you have more than one partner, change partners often, or have a partner who has more than one sexual partner, use condoms in addition to your regular contraception to reduce your risk of STIs. "It's about thinking of pregnancy risk and STI risk separately," says Caroline.

Long-acting reversible contraceptives (LARCs)

There are several types of LARC available in Australia. "They tend to be highly effective," says Caroline. "They don't have what we call a 'forgettability' factor, which means that for the prevention of pregnancy, they don't rely on action from the user daily or at the time of sex."

Although they tend to be cheaper than many other methods in the long term, the upfront cost can be a barrier for some women. They also need to be inserted and removed by a practitioner. Access to such health services can be a problem for some women.

Implants:

A contraceptive implant is a flexible, match-stick-sized rod inserted under the skin of the upper arm to slowly release the hormone progestogen. It is effective for up to three years. In Australia, the only type available is Implanon. It works by preventing ovulation (the release of an egg from the ovary); thickening the cervical mucus so sperm can't enter the uterus (womb) and changing the lining of the uterus to make it unsuitable for pregnancy.

Implanon is highly recommended for young women because it is more than 99.9 per cent effective and after insertion requires no action until it is time for removal. It is rapidly reversible and has no effect on future fertility, however it can cause irregular bleeding patterns while in use. The side effects associated with progestogen-based contraceptives (breast tenderness, headaches, acne, weight gain and mood changes) can also occur in some women.

Injections:

Contraceptive injections contain DMPA, a long-acting form of progestogen. The hormone is injected into a muscle every 12 weeks. As with other progestogen-based methods, it prevents pregnancy by stopping ovulation, thickening cervical mucus and changing the uterus lining. In Australia, DMPA is sold under the brand names Depo Provera and Depo Ralovera.

DMPA injections are highly effective at preventing pregnancy however a delayed return to normal fertility is common after injections stop. On average, women are able to conceive eight months after their last injection, but in some cases it can take up to 18 months for fertility to return. DMPA is also associated with a small loss of bone density however this is usually reversible after injections stop.

Intrauterine devices (IUDs):

An IUD is a small device that is inserted into the uterus through the vagina and cervix. There are two types available, both are 99.9 per cent effective. After insertion they require little-to-no attention until removal. Some women, particularly those who haven't had children, can find it uncomfortable to have an IUD inserted. A local anaesthetic or a light sedation can be used to minimise pain or discomfort.

Hormonal IUDs release a steady, low dose of progestogen into the uterus and are effective for up to five years. The only type available in Australia is called Mirena. They prevent pregnancy by thickening cervical mucus and thinning the uterus lining. As a result, they also significantly reduce menstrual flow. This can be helpful for women with heavy menstrual bleeding or cramping. As the progestogen is delivered directly into the uterus other typical progestogen-related side effects are rare.

Non-hormonal IUDs are made of plastic and copper and are effective for up to 10 years. The copper damages sperm, stopping ova (eggs) from becoming fertilised. Because they also prevent fertilised ova from implanting into the uterus lining they can be used as emergency contraception if inserted within five days of unprotected sex. They can cause longer, heavier periods initially but because they contain no hormones they don't cause hormone-related side effects.

IUDs are not recommended for women at high risk of STIs, and not all GPs are trained to insert and remove them. For more information and for contact details of Queensland practitioners who insert IUDs, call the Health Information Line on (07) 3216 0376.

Other contraceptives

Condoms:

Both male and female condoms create a physical barrier that prevents bodily fluids, such as sperm and vaginal fluid, from passing between sexual partners. If used correctly and consistently, they are effective at preventing pregnancy and STIs.

"They also have no side effects or contraindications and for some people that's a real advantage, particularly for women who are sensitive to or don't like taking hormonal methods of contraception." Female condoms are not as widely available as male condoms (you can get them at FPQ clinics, some pharmacies, and online). They are also slightly more expensive.

Combined oral contraceptive pill:

Commonly referred to as 'the pill', this daily oral contraceptive is a prescription medication. It contains synthetic forms of oestrogen and progestogen. It protects against pregnancy by stopping ovulation, thickening cervical mucus and changing the uterus lining. It is also used to treat painful or heavy periods, premenstrual syndrome, acne and endometriosis.

"If taken regularly, the pill is a very effective method," says Caroline. "It's fairly easy for most young women to get a prescription; it's user-controlled, so a woman can choose when she wants to start and stop it; and it has a predictable bleeding pattern." The disadvantages are that hormone-related side effects can occur in some women, and in typical use scenarios, the pill does have high failure rates. It has been estimated that one in five unplanned pregnancies may be due to women's lack of knowledge about the pill. Not knowing how it works, and therefore how it needs to be taken, can put women at risk of unplanned pregnancy. For more information, read our online article The pill: myths and misconceptions.

Progestogen-only pill:

Often referred to as 'the mini pill', this oral contraceptive is a prescription medication that needs to be taken at the same time each day – a pill is considered 'missed' if it is taken more than three hours late. Unlike the combined oral contraceptive pill, it contains only one hormone (progestogen). It protects against pregnancy by thickening cervical mucus and changing the uterus lining. It affects ovulation in some women.

"Its advantage is that it's just a low dose of progestogen so it doesn't have many contraindications," says Caroline. "Its disadvantage is that its efficacy relies very much on reliable pill taking, much more so than the combined pill, and as a result it can have a much higher failure rate. Its bleeding pattern is also less reliable."

Vaginal ring:

Available on prescription under the brand name NuvaRing, the vaginal ring is a small, flexible plastic ring that releases oestrogen and progestogen. It is inserted into the vagina on the first day of your period. You leave it in place for three weeks, then remove it for one week each month before replacing it with a new one. It can be a good choice for young women because it only needs to be used once a month. "It's similar to the pill in the way it works, but it only needs to be inserted once a month, rather than taken every day," says Caroline.

Diaphragm:

A diaphragm is a soft, dome-shaped rubber cap that is inserted into the vagina before sex. It covers the cervix, stoping sperm from entering the uterus. It must be left in place for at least six hours after sex, and is most effective when used with spermicide. Diaphragms must initially be fitted by a health practitioner, however once your correct size and type is known, you can buy them from most pharmacies.

Withdrawal:

This method involves withdrawing the penis from the vagina before ejaculation, so that sperm stays outside the vagina and away from external genitals. It is one of the least effective methods of birth control because proper timing of withdrawal is often difficult. Also, even if the penis is withdrawn in time, there is often pre-ejaculate fluid present and this can contain some sperm. Correct, consistent use requires co-operation from both partners.

Natural family planning methods:

These methods involve determining fertile and non-fertile days in your menstrual cycle and abstaining from vaginal sex, or using barrier methods of contraception, at 'unsafe' times. Young women commonly experience irregular periods, which can make it difficult to determine the 'safe' days. These methods require co-operation from both partners and women are advised to seek help from an experienced practitioner before relying on them.